Conventionally, an electric device for executing a process based on a map data is, for example, an in-vehicle device such as a navigation device, which is disclosed in JP-A-2008-241659 corresponding to US 2008/0243368. The in-vehicle device displays a map image on a display device, searches a guidance route to a destination, and guides the route or guides a road around a current position of the vehicle. A format of the map data is, for example, a KIWI format, which is disclosed in “Map data format KIWI for a vehicle navigation system,” in DENSO Technical Review, 2001, on Volume 6, Part 1, pages 29-34. With using this format, a road data is shown as a link and a node. A link data of each link for representing a link attribution such as a shape of a link and a street address is stored in the map data.
In a conventional map data, a unique link ID is assigned in each link. The link ID is used for linking a link data corresponding to the link ID with other data. For example, the link ID is used for representing a connection relationship of the link. In a conventional map data, for example, multiple link data are integrated into link sequence data. The link sequence data includes a node data showing a connection relationship of links with using the link ID. The node data relates to a node for connecting links. Further, information relating to existence of a traffic signal at an intersection corresponding to the node and traffic regulations such as right and/or left turn prohibition is stored in the node data.
Here, the conventional map data includes the link data relating to the link and the node data relating to the node, and therefore, the conventional map data includes information about coordinates of the link data and the node data, which is doubly held in the map data. Thus, the present inventors consider that information stored as the node data may be distributed and stored in the link data so that the node data can be deleted.
However, in the map data, when the node data is deleted, and the information about a connection relationship of links, which is previously stored as the node data, is distributed to and stored as the link data, it is required to refer to multiple link data so that information relating to the node such as the link connection relationship is obtained.
Accordingly, when the map data does not include the node data, a load of a process for detecting a condition of the node such as link connection relationship at the node increases.